Effects of boundary reflection on photoacoustic spectrum of porous silicon

Photoacoustic (PA) amplitude and phase spectra are studied on porous silico n (PS) samples. For the sample with a thinner PS layer and a rough interfac e observed by field-emission scanning electron microscope (FE-SEM), PA ampl itude decays rapidly at short wavelengths but stays at a higher level above 650 nm compared with a sample with a thicker PS layer and a smooth interfa ce. In this latter long-wavelength region, phase delay for the former sampl e is smaller. A model calculation for the two-layer model taking account of scattering of light in the porous media and interface reflection of light gives at least a qualitative explanation of these differences.